1. Field of the Invention
This invention relates to synthetic fibers useful, for example, as a partial or total replacement for cellulosic fibers in papermaking using conventional papermaking means. In particular, the invention relates to novel polymeric-inorganic mineral composite fibers useful for such purpose, to the manufacture of such fibers, preferably by wet spinning, and to the use thereof in papermaking.
2. Prior Art
Synthetic fibers are well known substitutes or additives for cellulosic fibers for papermaking. Acrylics, polyesters and polyamides are among the synthetic organic polymers that have been used. These materials have one or more detractive properties or characteristics. Most synthetic organic fibers require binders or heat treatment when employed in a papermaking operation since the fibers lack the self-binding properties of wood pulp fibers. Recently synthetic fibrillated polyethylene fibers and polystyrene-based papermaking fibers have been inroduced. These fibers do possess self-binding capability and they can be blended in any proportion with wood pulp to make paper products by conventional papermaking techniques. However, such fibers are composed solely of organic high polymers and, as such, are expensive in comparison to wood pulp.
Polyvinyl alcohol fibers are used commercially in papermaking and are particularly suitable for such use because polyvinyl alcohol possesses substantial capacity for hydrogen bonding. These fibers, however, are considerably more expensive than the polymeric organic fibers above mentioned, and the cost substantially exceeds that of wood pulp.
Inorganic fibers, notably those composed of glass, metal, ceramics and minerals, are used to make paper or paperlike products. These fibers are not self-binding and furthermore they are generally rigid or stiff. Therefore the inorganic fibers are limited to uses in which either specific properties such as flame resistance, chemical inertness, strength, or capability of formation from water-free furnishes outweigh the detractive properties mentioned above. Films and fibers composed completely of colloidal swelling clay (bentonite or montmorillonite) are also known but these fibers or films require special waterproofing treatment and do not possess the properties and handling characteristics of wood pulp fibers.
Mineral-filled filaments based on polyesters and nylon have been suggested for woven textile use, the fillers being special grades of kaolin clay which function to dull the sheen of stocking products. Generally the clay filler is used in relatively small amount, typically 2% by weight. Hot melt spinning is employed in the production of such mineral-filled filaments. Reference is made to the following patents: U.S. Pat. Nos. 3,366,597, 3,397,171, 3,526,609, 3,778,514, 3,673,147, Canada Pat. No. 756,672.
Canadian Pat. No. 745,220 teaches the dilution of polyamides used in making fibers or filaments with 20% to 40% by weight of minus 10 micron "hydrated Kaolin or Fullers earth." The fillers are used as cost savers and, in some cases, have a desirable effect on physical properties. Polymerization of the polyamide-yielding compounds preferably takes place in the presence of the hydrated mineral filler. The mixture of polymer and filler is formed into filaments or films by a conventional melt-extrusion technique. Use of more than 50% filler, based on the polyamide, increases the viscosity of the melt to an extent whereby it is difficult to extrude the mixture. The "Fuller's earth" and "kaolin", insofar as they are described in the patent, are minerals which correspond approximately to the formula Al.sub.2 O.sub.3.2SiO.sub.2.H.sub.2 O.